Industrial, agricultural and household systems use various types of valves for controlling fluid flow. The most common form of electrically operated valve employs a solenoid wound onto a bobbin, and a valve member located inside the bobbin and driven by a drive current passed through the solenoid. In a closed position, a tip of the valve member (armature) is pressed against a valve seat and thereby stops flow through a conduit in which the valve seat is disposed. Although the tip of the valve member is in many cases made of a synthetic resin, or other resilient material, other parts of the valve member are made up of a material having relatively high magnetic permeability, such as steel, so that it will be subject to force from the solenoid's magnetic field and will act as a solenoid armature.
In battery-operated actuators, electric valve-control circuitry should employ as little power as possible. To achieve highly energy efficient operation, the valve member (i.e., the solenoid's armature) needs to be as magnetically permeable as possible. Furthermore, the electric-valve control circuitry should apply only the minimum drive current necessary for the minimum duration during the armature activation for latching valves (i.e., valves whose actuators require power to open or close the valve but not to keep it opened or closed). In non-latching actuators, unnecessarily high drive current for holding the valve open also may needlessly reduce the battery's longevity. Therefore, the reduction of energy consumption is an important aspect of actuator design.
In many prior art actuators, water (or other fluid being regulated) can flow into the cavity of the bobbin containing the actuator. The actuator frequently includes a flow passage in communication with an internal void (i.e., armature chamber) to provide a low-flow resistance path and to compensate for the external pressure on the valve member (i.e., the pressure exerted by the regulated fluid onto the armature). Thus, the regulated fluid moves back and forth in response to closing or opening the actuator. This usually causes degradation of the armature (i.e., corrosion) and problems with metal and other ions (or other deposits) that accumulate within the bobbin's cavity. The severity of this problem depends on the type of fluid being regulated.
As mentioned above, an optimal armature of the solenoid has as high a magnetic permeability as possible. However, materials with very high magnetic permeability usually have low corrosion resistance. Thus, designers in the past have had to compromise permeability for corrosion resistance. For example, carbon steel has a high magnetic permeability, but is quite vulnerable to rust and corrosion. Therefore, designers have resorted to the higher magnetic permeability grades of stainless steel, even though stainless steel is less magnetically permeable than carbon steel. Still, designers have had problems with the above-described deposits, or conversely, problems with preventing fluid contamination of the armature, bobbin or other valve elements. Hence, the need for an improved valve actuator.